1. Field of the Invention
The present invention relates to probing apparatuses, probing circuit boards, and probing systems for high-voltage matrix probing; specifically to probing apparatuses, probing circuit boards, and probing systems that comprise a switching circuit, manufactured with a mixed high-voltage IC process, having the capability of probing a plurality of probe points.
2. Descriptions of the Related Art
In the manufacturing processes of various bare printed circuit board (PCB) products, such as PCBs or integrated circuit carrier boards, the conducting materials used in bare PCBs may not form the desired geometric shapes due to external factors, such as manufacturing techniques and operating environments. This probably leads to serious errors, such as a short circuit and a breakage circuit of the bare PCBs. If components are soldered on these defected bare PCBs, a great loss would be caused in a manufacturing process. Consequently, electrical tests including a short circuit test and a breakage circuit test should be performed to eliminate defects during the production of bare PCBs in order to improve the yield rate of delivered bare circuit boards so that the cost may be reduced.
Electrical tests of PCBs are usually done by test systems. Currently, these test systems for bare PCBs are classified into dedicated test systems, universal test systems and flying-probe test systems. The cost of a dedicated test system is lowest among them, but it requires longer manufacturing time and higher cost of test fixtures. The cost of a universal test system is higher than that of a dedicated test system, and it requires shorter manufacturing time and a lower cost of the test fixtures. Finally, the cost of a flying-probe test system is highest, and it requires no test fixture and has larger test areas. However, most flying-probe test systems hardly avoid a problem of significantly slow test speed.
For universal test systems, matrix probing is popular in the field of electrical test. The common way is to implement a matrix as a bed-of-nails as shown in FIG. 1A, which is a diagram of a single-density probe matrix of the prior art. Each circle in the figure represents a probe point, which usually connects with the conducting material of a bare PCB under test through a conductor for testing (such as a metal probing nail, a conducting rubber, etc.). A distance between two adjacent probe points is 100 mil (1 mil=0.00254 mm) as illustrated in FIG. 1A. Currently, a density of a probe matrix of the prior art can be one of a double-density probe matrix as shown in FIG. 1B, a quad-density probe matrix as shown in FIG. 1C, a octuple-density probe matrix as shown in FIG. 1D and a hexadecuple-density probe matrix as shown in FIG. 1E. The distance between two adjacent probe points is also marked in each figure. In the figures, probe points that are added to increase the density are represented in different patterns for better identification. In recent years, both the required density for probing and the relative number of probe points increase significantly.
Matrix probing requires a switching circuit to control the conductivity of each probe point. In general, each probe point is connected with two switch elements (such as bipolar transistors or field-effect transistors (FETs)) and each switch element is controlled by a switching circuit controller. FIG. 2 is a schematic diagram of a switching circuit of a bipolar transistor matrix of the prior art. The switching circuit comprises a plurality of PNP bipolar transistors 20, a plurality of probe points 21, a plurality of NPN bipolar transistors 22, a test signal input port 23, a switching circuit controller 24, a probing result output port 25, and a plurality of resistors 26. The plurality of PNP bipolar transistors 20 comprise a first PNP bipolar transistor 200, a second PNP bipolar transistor 201, a third PNP bipolar transistor 202, and a fourth PNP bipolar transistor 203. Each of the PNP bipolar transistors 200-203 comprises a base, an emitter, and a collector. The plurality of probe points 21 comprise a first probe point 210, a second probe point 211, a third probe point 212, and a fourth probe point 213 for electrically connecting with an external object under test (not shown). The plurality of NPN bipolar transistors 22 comprise a first NPN bipolar transistor 220, a second NPN bipolar transistor 221, a third NPN bipolar transistor 222, and a fourth NPN bipolar transistor 223. Each of the NPN bipolar transistors 220-223 comprises a base, an emitter, and a collector. The plurality of probe points 21 connect with the collectors of the first PNP bipolar transistor 200, the second PNP bipolar transistor 201, the third PNP bipolar transistor 202, and the fourth PNP bipolar transistor 203, respectively. Furthermore, the plurality of probe points 21 also connects with the collectors of the first NPN bipolar transistor 220, the second NPN bipolar transistor 221, the third NPN bipolar transistor 222, and the fourth NPN bipolar transistor 223, respectively. The switching circuit controller 24 comprises a first switching circuit controller 240 and a second switching circuit controller 241 and connects with the bases of the plurality of PNP bipolar transistors 20 and the bases of the plurality of NPN bipolar transistors 22 through one of the corresponding resistors 26 respectively to control on/off of the bipolar transistors 200-203 and 220-223. During the test process, a test signal is generated by an external test signal generation unit (not shown) and is then delivered to the emitters of all of the bipolar transistors 200-203 through the test signal input port 23. The first switching circuit controller 240 is used for controlling the connectivity of the bipolar transistors 200-203 so that the test signal inputted from the test signal input port 23 can be determined to be delivered to the corresponding plurality of probe points 21. The second switching circuit controller 241 selects at least one of the plurality of NPN bipolar transistors 22 to let a signal value from the corresponding the probe point pass its emitter and transmit to the probing result output port 25. Consequently, a probing result can be transmitted to an external verification unit (not shown) to determine whether a conductance of the object under test is as expected or not.
Here is an example to explain how to determine whether the object under test is conducted or not. Assume that the object under test has a metal conductor (not shown) connected between the first probe point 210 and the third probe point 212. To realize whether the metal conductor is actually conducted or not, a test can be done by turning on the first PNP bipolar transistor 200 through the first switching circuit controller 240 so that the test signal can be transmitted to the first probe point 210. At this time, the test signal is transmitted to the third probe point 212 through the metal conductor of the object under test. The second switching circuit controller 241 then turns on the third NPN bipolar transistor 222 to transmit a signal value from the third probe point 212 to the probing result output port 25. The external verification unit verifies the signal value. Assume that the test signal is a low-voltage signal from several volts to several tens volts and a resistance of the probe point is zero ohm. If the metal conductor of the object under test is conducted, the external verification unit should be able to measure a voltage value after a voltage drop on an equivalent resistance of the first PNP bipolar transistor 200, the metal conductor and the third NPN bipolar transistor 222. If the resistance of the metal conductor is too high due to, for example, manufacturing defects, the measured voltage value would be too low. In order to exclude defective parts of bare PCBs effectively, a standard can be established to determine whether a conductance condition of the metal conductor meets the standard of the manufacture of bare PCBs.
A test signal with a high voltage, such as 300 volts, is usually applied under the above-mentioned test. The high voltage is generated externally and inputted through the test signal input port 23. The bipolar transistors that correspond to unconducted probe points of the object under test are conducted through the switching circuit 24. The probing result of the probing result output port 25 is then measured by the external verification unit to determine whether acceptable isolation can be achieved between probe points that have no conductance. If some residues of the metal conductor unexpectedly connect probe points that should not be conducted due to manufacturing defects, a measured resistance would be too low and thus the defective condition can be verified.
FIG. 3 is a diagram of another switching circuit which comprises field-effect-transistors. The testing principle and method are similar to those shown in FIG. 2 and not described here.
In recent years, many mixed high-voltage IC processes, such as a BCD (Bipolar-CMOS-DMOS) process, a CD (CMOS-DMOS) process, and a BiCMOS (Bipolar-CMOS) process have been developed by many IC manufacturers. One of the features of these IC processes is to integrate a traditional low-voltage IC process (e.g. a CMOS process with a common operating voltage of 5 volts or below) and a medium-high voltage IC process (e.g. a series of processes of bipolar transistors or DMOS (Double-Diffused MOS) with a common operating voltage of several tens to approximately one thousand volts) into a single manufacturing process. Currently, many power component manufacturers, vehicle electronics manufacturers, and TFT LCD manufacturers adopt a mixed high-voltage IC process technique to develop new products that mix both CMOS and LDMOS (Lateral DMOS) or mix both CMOS and VDMOS (Vertical DMOS). These new products have the advantages of reducing packaging costs, reducing power consumptions and enhancing system performance.
In conclusion, in high-voltage matrix probing applications, since switch elements that support high voltages are required, low-voltage switching circuit controllers should be separated from high-voltage switch elements. This makes the bare PCBs of the switching circuits contain fewer circuits so that the probing density is limited. In addition to the problem of a larger area required, other problems include the number of control pins of the switching circuit is increased to control high-voltage switch elements. An example is shown in FIG. 2, wherein four probe points require eight switch elements and eight base control pins. That is, every probe point requires a pair of high-voltage switch elements and a pair of base control pins. Assuming that a SOT-23 package for the high-voltage switch elements is used, a probing system with two hundred thousand probe points in a common double-density matrix requires four hundred thousand high-voltage switch elements. Four hundred thousand base current-limiting resistors are also required. For the switching circuit controllers, four hundred thousand base control pins are required. Considering a PQ100 chip package, each chip has approximately 64 base control pins, excluding pins of the power and other control signals. Four hundred thousand base control pins requires 6,250 chips. If the size of a probing PCB is 28 cm×12 cm=336 cm2, required areas for the probing system are roughly calculated as Table 1 shows.
TABLE 1EquivalentUnit AreaRequiredTotal AreaNumber ofType of Components(mm2)Number(cm2)Probing PCBhigh-voltage switching8.9400,00035,600106.0element0805 chip film resistor4.5400,00018,000 53.6switching circuit910.0 6,25056,875169.3controller chipTotal110,499 328.9
Table 1 shows an amazing number of the probing PCBs required for the probing system. Furthermore, the calculation does not evaluate required areas for routing and other components (such as bypass capacitors, connectors and regulators, etc.). When the probing density reaches to a hexadecuple-density, the required number of probe points for the same probing area increases to approximately six times.